<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>display</title>
  </head>
  <style>
    div.ex1{
      width: 500px;
      margin: auto;
      border: 3px solid #73AD21;
    }
    div.ex2{
      max-width: 500px;
      margin: auto;
      border: 3px solid #73AD21;
    }
  </style>
  <body>
    <h2>CSS Max-width</h2>
    <div class="ex1">这个div元素的宽度是:500px</div>
    <br />
    <div class="ex2">这个div元素的最大宽度是:500px</div>
    <a></a>
  </body>
</html>
